Circular knitting machines have in general the disadvantage that, during operation, fibres, dust and other contaminants are deposited above all on the knitting tools, in the grooves receiving these and on the needle cams. When using specific yarns, e.g. those made of cotton, this fiber deposition occurs even more. The resulting tendency to contamination in high-performance machines, the needle cylinders of which are rotated at rotational speeds of 60 rpm and more, is particularly critical. The degree of contamination here is already so great after a running time of a few hours that cleaning operations are imperative.
In the case of circular knitting machines of the initially described type which operate according to relative technology and in which knitting needles and knocking-over/holding-down sinkers are moved in opposite directions during loop formation, dedusting devices are hence already known (DE 35 32 856 C1) which have at least one opening penetrating a cam segment, through which opening a compressed air flow is directed. This opening is directed essentially radially and diagonally from the bottom and outwardly to the top and inwardly in such a manner that it opens into an annular space which is disposed above the pivot points of the sinkers and between the rear sides of the sinkers and the needle cylinder. By such means it is intended to avoid that fibres and dust are deposited in the sinker grooves and are compacted there. According to knowledge obtained in practice with such machines, these measures are however not adequate for effective dust removal. It is to note in this respect that the expressions “dust removal” and “dedusting” are intended to mean within the scope of the present invention both the subsequent removal of already deposited fibres and dust particles and the keeping clean, i.e. preventing deposition of these particles.
In addition, circular knitting machines with dedusting devices are known, in which the entire cam housing is surrounded by an essentially closed housing. Compressed air is introduced from outside into this housing. In the case of a circular rib knitting machine, the compressed air from the housing is directed for example into an annular gap between the needle cylinder and a dial assigned thereto (DE-PS 15 85 177). In contrast, the compressed air from the housing passes in the case of single machines e.g. into an annular gap which is configured between an upper region of the needle cylinder and a sinker ring which is mounted on the latter by means of radial webs (e.g. EP 0 816 546 B1). Even these two types of dedusting, as tests have shown, are inadequate in the case of high-performance machines. In addition, they have the additional disadvantage that the closed housing makes access to the circular knitting machine difficult, and the housing must be opened or removed before operations can be performed on different functional parts, e.g. on the needle cams for the purpose of changing the loop size.
In addition, numerous further dedusting devices which operate with compressed air are known, said devices likewise effecting however either inadequate dedusting and/or demanding complicated and hence expensive and undesired changes to the circular knitting machine (e.g. DE-OS 16 35 796 and DE-OS 16 35 836).